U.S. patent application number 09/940424 was filed with the patent office on 2002-04-25 for liquid crystal display apparatus.
Invention is credited to Hirata, Mitsuaki, Ikeguchi, Tazo, Mizushima, Shigeaki, Morimoto, Mitsuaki, Shimoshikiryoh, Fumikazu.
Application Number | 20020047958 09/940424 |
Document ID | / |
Family ID | 18748370 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020047958 |
Kind Code |
A1 |
Hirata, Mitsuaki ; et
al. |
April 25, 2002 |
Liquid crystal display apparatus
Abstract
An object of the invention is to provide a high-contrast liquid
crystal display apparatus which is excellent in display quality,
with its substrates equally spaced with high accuracy. On a first
and a second substrate are formed a color filter of three colors:
red, green, and blue, electrodes for applying a voltage to a liquid
crystal layer, orientation film layers for orienting liquid
crystal, a pair of polarizing plates arranged in a crossed Nicol
state, a TFT element, and a wire (not shown) The substrates are
bonded together with spherical spacers interposed therebetween,
thereby constituting the liquid crystal layer. Then, the spherical
spacers are selectively placed in the color filter regions of red-
and blue-color.
Inventors: |
Hirata, Mitsuaki; (Nara-shi,
JP) ; Shimoshikiryoh, Fumikazu; (Tenri-shi, JP)
; Mizushima, Shigeaki; (Ikoma-shi, JP) ; Morimoto,
Mitsuaki; (Tenri-shi, JP) ; Ikeguchi, Tazo;
(Tenri-shi, JP) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
8th Floor
1100 North Glebe Road
Arlington
VA
22201-4714
US
|
Family ID: |
18748370 |
Appl. No.: |
09/940424 |
Filed: |
August 29, 2001 |
Current U.S.
Class: |
349/106 |
Current CPC
Class: |
G02F 1/13392 20130101;
G02F 1/133757 20210101; G02F 1/133514 20130101 |
Class at
Publication: |
349/106 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2000 |
JP |
2000-260345 |
Claims
What is claimed is:
1. A liquid crystal display apparatus comprising: a first and a
second substrate, of which at least one is transparent; color
filters of a plurality of colors formed on at least one of the
substrates; a spacer for defining a gap between the first and
second substrates, wherein a density of spacers existing in a color
filter region of any one of the colors is lower than a density of
spacers existing in a color filter region of at least one of
remaining colors.
2. A liquid crystal display apparatus comprising: a first and a
second substrate, of which at least one is transparent; a color
filter of a plurality of colors formed on at least one of the
substrates; a liquid crystal layer contained between the first and
second substrates; and a spacer for defining a gap between the
first and second substrates, wherein, in the liquid crystal layer,
display picture element regions have at least two regions which
have mutually different liquid crystal molecule orientations, and
wherein a density of spacers existing in a color filter region of
any one of the colors is lower than a density of spacers existing
in a color filter region of at least one of remaining colors.
3. The liquid crystal display apparatus of claim 1, wherein a
density of spacers existing in a color filter region of a color
having higher visibility for human eyes is lower than a density of
spacers existing in a color filter region of a color having lower
visibility for human eyes.
4. The liquid crystal display apparatus of claim 2, wherein the
density of spacers existing in the color filter region of a color
having higher visibility for human eyes is lower than the density
of spacers existing in the color filter region of a color having
lower visibility for human eyes.
5. The liquid crystal display apparatus of claim 1, wherein the
color filters are of three colors: red, green, and blue, and a
density of spacers existing in a color filter region of green-color
is lower than a density of spacers existing in a color filter
region of red-or blue-color.
6. The liquid crystal display apparatus of claim 2, wherein the
color filters are of three colors: red, green, and blue, and a
density of spacers existing in a color filter region of green-color
is lower than a density of spacers existing in a color filter
region of red-or blue-color.
7. The liquid crystal display apparatus of claim 1, wherein the
color filters are of three colors: red, green, and blue, and a
density of spacers existing in a color filter region of green-or
blue-color is lower than a density of spacers existing in a color
filter region of red-color.
8. The liquid crystal display apparatus of claim 2, wherein the
color filters are of three colors: red, green, and blue, and a
density of spacers existing in a color filter region of green-or
blue-color is lower than a density of spacers existing in a color
filter region of red-color.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a liquid crystal display
apparatus for use as a monitor display in a computer and for
displaying a video image or the like, and more particularly to a
liquid crystal display apparatus which is excellent in display
quality and visual angle characteristics.
[0003] 2. Description of the Related Art
[0004] White/black display brightness contrast (hereafter simply
referred to as "contrast") is relevant to the display quality of a
liquid crystal display apparatus. Causes of degrading the contrast
include a phenomenon in which light leaks through spherical spacers
or through the vicinity thereof when a black color is displayed. As
techniques to eliminate degradation of contrast due to such a
light-leakage phenomenon, for example, a liquid crystal display
apparatus disclosed in Japanese Unexamined Patent Publication JP-A
2-15241 (1990), a method for manufacturing a liquid crystal display
panel disclosed in Japanese Unexamined Patent Publication JP-A
4-204417 (1992), and others are known.
[0005] The liquid crystal display apparatus disclosed in JP-A
2-15241 comprises a thin-film transistor substrate including a
substrate and thin-film transistor arrays arranged in a matrix form
thereon, and a counter electrode substrate including a transparent
substrate, and a transparent counter electrode and a transparent
insulating film formed on a transparent substrate. In this
construction, a gap between the thin-film transistor substrate and
the counter electrode substrate is defined with conductive columns
formed on source electrode lines of the transistors by
vapor-deposition, sputtering or the like. On the other hand, in the
method for manufacturing a liquid crystal display panel disclosed
in JP-A 4-204417, spacer particles are positively or negatively
charged, the transparent electrode formed on a glass substrate is
given the same pole as that of the spacer particle, and the spacer
particles are dispersed. In this way, by forming and dispersing
spacers on the underside of a light-shielding material, such as a
metal wire, an active element, or a black mask, or on a pattern
gap, i.e., a region other than the display electrode region, it is
possible to prevent occurrence of light leakage due to a
spacer.
[0006] However, the liquid crystal display apparatus disclosed in
JP-A 2-15241 and the method for manufacturing a liquid crystal
display panel disclosed in JP-A 4-204417 have the following
disadvantages. The former requires a column forming process, and,
in this regard, unevenness in the heights of columns inconveniently
causes a gap between the substrates to become uneven. This makes it
difficult to realize a liquid crystal display apparatus in which
the substrates are equally spaced with high accuracy. The latter
requires a light-shielding portion to have an area large enough to
disperse spherical spacers. This accordingly imposes a restriction
on the size of the opening portion excluding the light-shielding
portion. Consequently, it is difficult to increase the
transmittance of the liquid crystal display apparatus.
[0007] Moreover, there arises another problem. Due to the
wavelength-dependent property existing in the spectral
characteristics of a polarizing plate, liquid crystal, a phase
difference plate, and other materials, the black display of a
liquid crystal display apparatus is tinged with blue. Since the
bluish tint occurs only in black display, there is a problem that
if color adjustment is performed to solve this bluish tint problem,
the color of white display also varies.
[0008] Furthermore, in a liquid crystal display apparatus with a
wide viewing angle comprising: a liquid crystal layer having a
display picture element region including a first and a second
region having mutually different liquid crystal molecule
orientations; and a phase difference compensating element for
compensating for, in a state where no voltage is applied, the
refractive index anisotropy of the liquid crystal molecules aligned
substantially parallel to the substrate surface, light leakage due
to a spherical spacer is more notable and the bluish tint of black
display is deeper than in a common twisted nematic mode
construction.
SUMMARY OF THE INVENTION
[0009] An object of the invention is to provide a liquid crystal
display apparatus offering high contrast and excellent display
quality, with its substrates equally spaced with high accuracy.
[0010] The invention provides a liquid crystal display apparatus
comprising:
[0011] a first and a second substrate, of which at least one is
transparent;
[0012] color filters of a plurality of colors formed on at least
one of the substrates;
[0013] a spacer for defining a gap between the first and second
substrates,
[0014] wherein a density of spacers existing in a color filter
region of any one of the colors is lower than a density of spacers
existing in a color filter region of at least one of remaining
colors.
[0015] According to the invention, the density of the spacers
existing in the color filter region of any one of the colors is
lower than that of the spacers existing in the color filter region
of the at least one of remaining colors. This arrangement helps
prevent occurrence of light leakage due to the spacer and thus
makes it possible to keep the brightness of black display low and
to improve the contrast.
[0016] As described heretofore, according to the invention, light
leakage due to a spacer can be successfully prevented. This makes
it possible to keep the brightness of black display low, to allow
substrates to be equally spaced with high accuracy, to obtain
higher transmittance, and to improve the contrast.
[0017] The invention further provides a liquid crystal display
apparatus comprising:
[0018] a first and a second substrate, of which at least one is
transparent;
[0019] a color filter of a plurality of colors formed on at least
one of the substrates;
[0020] a liquid crystal layer contained between the first and
second substrates; and
[0021] a spacer for defining a gap between the first and second
substrates,
[0022] wherein, in the liquid crystal layer, display picture
element regions have at least two regions which have mutually
different liquid crystal molecule orientations,
[0023] and wherein a density of spacers existing in a color filter
region of any one of the colors is lower than a density of spacers
existing in a color filter region of at least one of remaining
colors.
[0024] According to the invention, there is provided a liquid
crystal layer in which display picture element regions have at
least two regions having mutually different liquid crystal molecule
orientations. Moreover, the density of spacers existing in the
color filter region of any one of the colors is lower than the
density of spacers existing in the color filter region of at least
one of remaining colors. This arrangement makes it possible to
attain wide-angle-view characteristics and to prevent occurrence of
light leakage due to a spacer. Consequently, the brightness of
black display is kept low and the contrast is improved.
[0025] Further, according to the invention, wide-angle-view
characteristics are attained and occurrence of light leakage due to
a spacer can be prevented. This makes it possible to keep the
brightness of black display low, to allow substrates to be equally
spaced with high accuracy, to obtain higher transmittance, and to
improve the contrast.
[0026] Further, in the invention, it is preferable that a density
of spacers existing in a color filter region of a color having
higher visibility for human eyes is lower than a density of spacers
existing in a color filter region of a color having lower
visibility for human eyes.
[0027] According to the invention, the density of spacers existing
in the color filter region of a color having higher visibility for
human eyes is lower than the density of spacers existing in the
region corresponding to a color having lower visibility for human
eyes. This helps prevent light leakage due to a spacer from
occurring in light of a color having higher visibility for human
eyes, and thereby keep the brightness of black display low and
improve the contrast.
[0028] In the invention, it is preferable that the color filters
are of three colors: red, green, and blue, and that a density of
spacers existing in a color filter region of green-color is lower
than a density of spacers existing in a color filter region of
red-or blue-color.
[0029] According to the invention, the density of spacers existing
in the color filter region of green-color is lower than the density
of spacers existing in the color filter region of red-or
blue-color. This helps prevent light leakage due to a spacer from
occurring in green light having higher visibility for human eyes,
and thus keep the brightness of black display low and improve the
contrast.
[0030] Further, according to the invention, light leakage due to a
spacer is prevented from occurring in green light having higher
visibility for human eyes. This makes it possible to keep the
brightness of black display low and to improve the contrast.
[0031] In the invention, it is preferable that the color filters
are of three colors: red, green, and blue, and that a density of
spacers existing in a color filter region of green-or blue-color is
lower than a density of spacers existing in a color filter region
of red-color.
[0032] According to the invention, the density of spacers existing
in the color filter region of green-or blue-color is lower than the
density of spacers existing in the color filter region of
red-color. This helps prevent light leakage due to a spacer from
occurring in green light having higher visibility for human eyes
under photopic conditions of vision and in blue light having higher
visibility for human eyes under scotopic conditions of vision.
Consequently, the brightness of black display is kept low, the
contrast is improved, and a bluish tint is suppressed.
[0033] Moreover, according to the invention, it is possible to
prevent light leakage due to a spacer from occurring in green light
having higher visibility for human eyes under photopic conditions
of vision and in blue light having higher visibility for human eyes
under scotopic conditions of vision. Consequently, the brightness
of black display is kept low, the contrast is improved, and a
bluish tint is suppressed
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Other and further objects, features, and advantages of the
invention will be more explicit from the following detailed
description taken with reference to the drawings wherein:
[0035] FIG. 1 is a sectional view illustrating the structure of a
liquid crystal display apparatus 10 of an embodiment of the
invention;
[0036] FIG. 2 is a sectional view illustrating the structure of a
liquid crystal display apparatus 20 of the embodiment of the
invention;
[0037] FIG. 3 shows luminosity curve which indicates the
relationship between the relative luminosity of human eyes and the
wavelength of light;
[0038] FIG. 4 is a sectional view illustrating the structure of a
liquid crystal display apparatus 40 of another embodiment of the
invention;
[0039] FIG. 5 is a view showing the optical characteristics of the
invention; and
[0040] FIGS. 6A to 6C are views showing a transfer-based placement
method for a spherical spacer 106.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] Now referring to the drawings, preferred embodiments of the
invention are described below.
[0042] FIG. 1 is a sectional view illustrating the structure of a
liquid crystal display apparatus 10 of an embodiment of the
invention. The example shown in FIG. 1 is a light transmission-type
TFT (Thin Film Transistor) active matrix liquid crystal display
apparatus in a twisted nematic mode.
[0043] Note that the display mode employed in the liquid crystal
display apparatus of the invention is not limited to the twisted
nematic mode. For example, it is possible to employ instead an ECB
(Electrically Controlled Birefringence) mode, a vertical
orientation mode, a transverse electric field mode, a high
molecular dispersion liquid crystal mode, an OCB (Optically
self-Compensated Birefringence) mode, or any other liquid crystal
display mode in which the action of liquid crystal is controlled by
an electric field. Note also that the active element is not limited
to a TFT but may be a diode, that the driving method is not limited
to an active driving method but may be a duty driving method, and
that the display pattern may be either a reflection or a
semi-reflection pattern.
[0044] The liquid crystal display apparatus 10 is provided with: a
first and a second substrate 100a and 100b, of which at least one
is transparent; a liquid crystal layer 101; a color filter 102 of
several colors formed on the first substrate 100a; electrodes 103a
and 103b for applying a voltage to the liquid crystal layer 101;
orientation film layers 104a and 104b for orienting liquid crystal;
a pair of polarizing plates 105a and 105b arranged in a crossed
Nicol state; a TFT element; and a wire (not shown). The thickness
of the liquid crystal layer 101 is defined by a spherical spacer
106 sandwiched between the substrates 100a and 100b.
[0045] Note that, to improve the display quality and reliability,
in addition to the above stated constituent elements, for example,
a phase difference plate (a phase difference compensation film, a
liquid crystal cell, or any other element may be used instead as
long as it offers adequate refractive index anisotropy) may be
disposed inside the polarizing plates 105a and 105b. Moreover,
additional arrangement of a planarizing film for planarizing the
color filter, a light-shielding mask, or the like is possible.
[0046] In this embodiment, the color filter 102 is of three colors:
red, green, and blue. The spherical spacers 106 are placed only in
the color filter regions of blue- and red-color and are not placed
in the color filter region of green-color, or are placed therein
slightly, if any.
[0047] The contrast of a liquid crystal display apparatus is
defined by the ratio of the brightness of white display to the
brightness of black display. The brightness is expressed as a value
corresponding to the relative luminosity characteristic of human
eyes. FIG. 3 shows a luminosity curve which indicates the
relationship between the relative luminosity of human eyes and the
wavelength of light. As will be understood from the curve depicted
in the figure, the light of 500 nm in wavelength, which corresponds
to green light, has the highest visibility for human eyes.
[0048] A liquid crystal display apparatus customarily employs a
color filter of three colors: red, green, and blue. From the
standpoint of the relative luminosity of human eyes, it can be
considered that the contrast of a liquid crystal display apparatus
depends mainly on the transmission characteristics of the color
filter region of green-color.
[0049] Accordingly, by making the density of spacers, i.e., the
number of spacers per unit area, existing in the color filter
region of green-color lower than the density of spacers existing in
the color filter region of red-or blue-color, it is possible to
prevent light leakage from occurring in the color filter region of
green-color and thus achieve contrast that is substantially equal
to the contrast obtained when no spherical spacer exists.
[0050] Also in a case where a color filter of different colors than
red, green, and blue, for example, a color filter of white, which
serves to increase brightness, cyan, magenta, and yellow is used,
based on the similar theory, by decreasing the density of spherical
spacers existing in the color filter region of a color
corresponding to approximately 550 nm in wavelength, the contrast
is improved.
[0051] Moreover, eliminating spherical spacers from the color
filter region of blue-color helps suppress a bluish tint that
occurs in the black display due to the existence of
wavelength-dependent property in the spectral characteristics of a
polarizing plate, liquid crystal, a phase difference plate, and
other materials. In addition, as seen from the relative luminosity
observed under photopic conditions of vision shown in FIG. 3, at a
dark place, human eyes are particularly sensitive to a blue color.
Therefore, eliminating spherical spacers from the blue-color region
allows the advantage of the invention to become more evident.
[0052] Next, the invention will be described below in detail by way
of embodiments.
[0053] (Embodiment 1)
[0054] The substrates 100a and 100b are built as a counter
electrode substrate and an active element substrate, respectively.
The counter electrode substrate 100a employed in this embodiment is
of similar construction to a conventional one on which a color
filter 102 of three colors RGB (red, green, and blue) is formed in
the shape of a stripe. Note that a delta arrangement may be adopted
here for the color filter, or the color filter may be formed on the
active element substrate. On the color filter 102 is formed a
transparent electrode made of ITO (Indium Tin Oxide). Although the
active element substrate 100b employed in the embodiment has
basically the same structure as that of conventional ones, it needs
to be designed as follows. Like a conventional active element
substrate, on the substrate is formed a TFT acting as an active
element, signal lines that correspond to their respective colors R,
G, and B, and a scanning line. To examine defects found in the
active element substrate or in the conditions of the liquid crystal
display apparatus, the three signal lines corresponding to their
respective colors R, G, and B of the color filter 102 are
individually short-circuited outside the active area, and, after
being subjected to examinations, the short-circuit lines are cut
off.
[0055] On the two substrates are formed orientation films 104a and
104b for orienting liquid crystal. To control the orientation,
rubbing treatment is conducted therefore.
[0056] Now, a description will be given below as to a placement
method for selectively placing the spherical spacer 106 on the
active element substrate 100b. A negative potential is imposed on
the signal line corresponding to the green color of the color
filter 102, a positive potential is imposed on the signal line
corresponding to the other color thereof, and a positive potential
is imposed on the scanning line. Material designing and the setting
of dispersion condition for the spacer are determined such that the
surface potential of the spherical spacer 106 to be dispersed is
negatively charged. Consequently, by dint of Coulomb force, the
spherical spacers 106 are selectively placed in the red- and
blue-color regions.
[0057] A picture element, acting as a display region, generally has
a width of about 100 .mu.m. Even the smallest one has a width in
the range of 30 to 40 .mu.m. Therefore, the spherical spacers 106a
are selectively placed with ease by the above stated dispersing
method. Moreover, where the opening ratio is increased to 80%,
assuming that the width of the picture element is 100 .mu.m, the
width of the light-shielding portion lying between adjacent picture
elements is set at no greater than 10 .mu.m. In this case,
selective placement of the spacer in the light-shielding portion is
difficult by the prior art method. However, with the technique
underlying the invention, the spherical spacers 106 can be placed
in the red- and blue-color regions. This makes it possible to keep
the opening ratio greater than 80%, thereby achieving sufficiently
high transmittance.
[0058] Note that, in connection with the above stated potential
setting, it is essential only that the surface potential of the
signal line corresponding to a color region where no spherical
spacer 106 is intended to be placed and that of the spherical
spacer 106 have the same sign. More specifically, when the
spherical spacer 106 is positively charged, a negative potential is
imposed on the scanning line and the signal line corresponding to a
color region where the spherical spacer 106 is intended to be
placed, and a positive potential is imposed on a picture element
corresponding to a color region where no spherical spacer 106 is
intended to be placed.
[0059] Moreover, for the dispersion of the spherical spacers 106,
the embodiment employs a method of applying an electrical charge
and exploiting Coulomb force. However, any other method may be
employed instead, for example, either a method whereby, after the
dispersion of the spacers, only those existing in the targeted area
are removed or a method whereby, after the spacers to be left are
bonded to the surface of the substrate, only those existing in the
targeted area are removed by air-blowing or other means, or a
combination of these methods.
[0060] As another method for placing the spherical spacer 106,
there is known a transfer-based method as shown in FIGS. 6A, 6B,
and 6C. Firstly, the spherical spacers 106 are dispersed on a
transfer plate 601 provided with a projection having a pitch equal
to the pitch of the color filter 102 of one and the same color (see
FIG. 6A). Secondly, the projection of the transfer plate 601 is
aligned with the region of the counter electrode substrate 100a
where the spherical spacers 106 are intended to be placed, thereby
bringing the transfer plate 601 into contact with the counter
electrode substrate 100a (see FIG. 6B). Lastly, the transfer plate
601 is detached from the counter electrode substrate 100a, and as a
result the spherical spacers 106 are placed by transfer in any
given region of the counter electrode substrate 100a (see FIG. 6C).
At the time when the spherical spacers 106 are dispersed on the
transfer plate 601, by charging the projection and the spherical
spacer 106 so that they have different signs, the spherical spacers
106 can be effectively collected in the projection of the transfer
plate 601. However, this can be achieved without the charging.
[0061] In any of the above stated methods, in order for the
spherical spacers 106 to be securely fixed to the substrate, it is
preferable to use such spherical spacers as exhibit adhesion
properties by heat or light application with respect to a
substrate.
[0062] In this way, after the spherical spacers 106 are selectively
placed in the red-and blue-color regions, the two substrates are
bonded together, and then a liquid crystal material is injected
thereinto. Upon completion of sealing of the inlet, examinations
for the panel and a cut-off process for the aforesaid short
circuits used for examinations are conducted. Thereafter, the
polarizing plates 105 a and 105b are bonded together and the
periphery circuits are mounted, and eventually the liquid crystal
display apparatus 10 is realized.
[0063] According to the embodiment, a 10% improvement of the
contrast is achieved.
[0064] (Embodiment 2)
[0065] As another embodiment, a construction is shown in FIG. 2
wherein spherical spacers 206 are placed only in the red-color
region. A liquid crystal display apparatus 20 is, like the liquid
crystal display apparatus 10, provided with: a first and a second
substrate 200a and 200b; a liquid crystal layer 201; a color filter
202 of a plurality of colors formed on the first substrate 200a;
electrodes 203a and 203b for applying a voltage to the liquid
crystal layer 201; orientation film layers 204a and 204b for
orienting liquid crystal; a pair of polarizing plates 205a and 205b
arranged in a crossed Nicol state; a TFT element; and a wire (not
shown). The thickness of the liquid crystal layer 201 is defined by
a spherical spacer 206 sandwiched between the substrates 200a and
200b.
[0066] The liquid crystal display apparatus 20 of this embodiment
is manufactured based on a method similar to that adopted in the
embodiment 1.
[0067] In this embodiment, it is possible to prevent light leakage
from occurring only in the red-color region which has lower
luminosity under either photopic or scotopic conditions of vision.
As a result, there is provided a high-contrast liquid crystal
display apparatus 20 in which no tint was perceived in the black
display under subjective evaluation.
[0068] FIG. 4 is a sectional view illustrating the structure of a
liquid crystal display apparatus 40 of another embodiment of the
invention.
[0069] The liquid crystal display apparatus 40 is provided with: a
first and a second substrate 400a and 400b, of which at least one
is transparent; a liquid crystal layer 401 sandwiched between the
first and second substrates 400a and 400b, the liquid crystal layer
being made of a nematic liquid crystal material having positive
dielectric anisotropy; a color filter 402 of a plurality of colors
formed on at least one of the substrates; a first and a second
electrode 403a and 403b disposed in the first and second substrates
400a and 400b, respectively, for applying to the liquid crystal
layer 401 an electric field which is substantially perpendicular to
the first and second substrates 400a and 400b; orientation film
layers 404a and 404b for orienting liquid crystal; a first and a
second polarizing plate 405a and 405b disposed on the outer sides
of the first and second substrates 400a and 400b, respectively, the
polarizing plates being arranged in a crossed Nicol state; phase
difference compensating elements 407a and 407b (a phase difference
compensation film, a liquid crystal cell, or any other element may
be used instead as long as it offers adequate refractive index
anisotropy) disposed on the inner sides of the polarizing plates
405a and 405b, respectively; and phase difference compensating
elements 408a/409a and 408b/409b disposed on the outer sides of the
phase difference compensating elements 407a and 407b,
respectively.
[0070] Note that the phase difference plates 407a, 407b, 408a,
408b, 409a, and 409b may be omitted, or used singly or in
combination.
[0071] The thickness of the liquid crystal layer 401 is defined by
a spherical spacer 406 sandwiched between the substrates 400a and
400b.
[0072] In the liquid crystal layer 401, each display picture
element region has at least a first and a second domain (region)
having mutually different liquid crystal molecule orientations. The
phase difference compensating elements 407a to 409b, in a state
where no voltage is applied, compensate for the refractive index
anisotropy of the liquid crystal molecules aligned substantially
parallel to the surfaces of the first and second substrates 400a
and 400b.
[0073] The liquid crystal display apparatus 40 of this embodiment
is of the type that provides a wide viewing angle. In this
apparatus, as compared with a twisted nematic mode construction,
the light passing through spherical spacers is large in quantity.
This allows the advantage of the invention to become more
evident.
[0074] In this embodiment, the color filters 402 are of three
colors of red, green, and blue. The spherical spacers 406 are
placed only in the blue- and red-color regions, and are not placed
in the green-color region, or are placed slightly therein, if
any.
[0075] (Embodiment 3)
[0076] Next, a description will be given below as to, as still
another embodiment, a liquid crystal display apparatus with a wide
viewing angle to which the invention is applied. Note that a
manufacturing method therefore is similar to that adopted in the
embodiments 1 and 2 and thus the description thereof will be
omitted.
[0077] The optical characteristics of this embodiment will be
concretely described with reference to FIGS. 4 and 5. Elliptic
figures depicted in FIG. 5 schematically represent liquid crystal
molecules, and arrows represent the axis (retardation axis having
the maximum refractive index) for the ellipsoid of refractive index
of each phase difference plate (each has positive optically
uniaxial characteristics) . Arrows observed in the polarizing
plates 505a and 505b represent the polarization axis (the
transmission axis) of the polarizing plate.
[0078] As shown in FIG. 5, in the liquid crystal layer 501, each
display picture element region has a first domain 501a and a second
domain 501b that have mutually different orientation states. In the
example shown in FIG. 5, of the liquid crystal molecule within the
first domain 501a and the liquid crystal molecule within the second
domain 501b have their directors oriented at azimuth angles
different from each other by 180 degrees. Accordingly, when a
voltage is applied between the electrodes, the liquid crystal
molecules within the first domain 501a stand up in a clockwise
direction, and the liquid crystal molecules within the second
domain 501b stand up in a counterclockwise direction. That is, the
orientations of the liquid crystal molecules are so controlled that
the liquid crystal molecules within one domain and those within the
other domain stand up in different directions. Such orientations of
liquid crystal molecule directors can be realized by means of
well-known techniques using an orientation film.
[0079] By forming a plurality of the first and second domains
having director orientation directions 180 degree different form
each other in a single display picture element region, it is
possible to make the visual angle characteristics uniform more
satisfactorily. Note that the division of orientation need not be
limited to two-division orientation. It is essential only that, in
the entire display area in a voltage-applied state, the sum of the
areas of the regions where liquid crystal molecules stand up in one
direction be equal to the sum of the areas of the regions where the
same stand up in the other direction. In consideration of evenness
in the display, it is preferable to make the unit for the division
of orientation as small as possible. Specifically, it is preferable
that the orientation is divided into two or more portions in each
pixel region.
[0080] The phase difference plates 507a and 507b each have positive
uniaxial refractive index anisotropy. The retardation axis
(indicated by the arrows in the figure) thereof is arranged
orthogonal to the retardation axis of the liquid crystal layer 501
in a state where no voltage is applied. This arrangement helps
prevent occurrence of light leakage due to the refractive index
anisotropy exerted by the liquid crystal molecules in a state where
no voltage is applied, and consequently, black display (normally
black characteristics) is obtained. Note that the black display can
also be obtained by using one of the two phase difference plates
507a and 507b.
[0081] The phase difference plates 508a and 508b each have positive
uniaxial refractive index anisotropy. The retardation axis
(indicated by the arrows in the figure) thereof is arranged
perpendicular to the surface of the substrate, i.e., perpendicular
to the retardation axes of the liquid crystal layer 501 and the
phase difference plates 507a and 507b. These phase difference
plates compensate for variation in the transmittance due to the
change of the visual angle, and, during the black display in
particular, suppress light leakage accompanied by the change of the
visual angle (the blurred black tone). Accordingly, by providing
the phase difference plates 508a and 508b, a liquid crystal display
apparatus can be realized that offers more excellent visual angle
characteristics. Note that the phase difference plates 508a and
508b do not necessarily have to be provided, or it is also possible
to use only one of them to achieve the desired effect.
[0082] The phase difference plates 509a and 509b each have positive
uniaxial refractive index anisotropy. The retardation axis
(indicated by the arrows in the figure) thereof is arranged
orthogonal to the polarization axis of the polarizing plate i.e.,
arranged at 45.degree. with respect to the retardation axes of the
liquid crystal layer 501 and the phase difference plates 507a and
507b. These phase difference plates compensate for the rotation of
the polarization axis of elliptically polarized light. Accordingly,
by providing the phase difference plates 509a and 509b, display
with more excellent visual angle characteristics can be realized.
Note that the phase difference plates 509a and 509b do not
necessarily have to be provided, or it is also possible to use only
one of them to achieve the desired effect.
[0083] The above stated phase difference plates do not necessarily
have to have uniaxial refractive index anisotropy but may have
positive biaxial refractive index anisotropy. Moreover, a
planarizing film for planarizing the color filter, a
light-shielding mask, or the like may be additionally provided
within the liquid crystal display apparatus 40.
[0084] This embodiment is so designed that the spherical spacers
406 are placed only in the blue- and red-color regions and are not
placed in the green-color region, or are placed therein slightly,
if any, otherwise they are placed only in the red-color region.
[0085] Moreover, as described above, in the embodiment, due to the
normally black characteristics of compensating for the refractive
index anisotropy of liquid crystal molecules as observed in a state
where no voltage is applied, a spherical spacer with no phase
difference allows transmission of light, and therefore the light
leakage due to the spherical spacer occurring in the blue- and
red-regions becomes notable. As a result, the degree of the
degradation of contrast becomes greater compared to that observed
in a twisted nematic mode construction. Accordingly, with the
present invention, the construction with a wide viewing angle of
the embodiment, in contrast to a common twisted nematic mode
construction which provides a 10% improvement in contrast, provides
twice the contrast ratio. Further, as compared with a common
twisted nematic mode construction, a liquid crystal display
apparatus with a wide viewing angle employs a larger number of
phase difference films and thus tends to suffer from a bluish tint.
In the embodiment, however, by placing spherical spacers only in
the red-color region, it is possible to satisfactorily suppress a
bluish tint occurring in the black display and thus improve the
display quality significantly.
[0086] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The present embodiments are therefore to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description and all changes which come within the meaning
and the range of equivalency of the claims are therefore intended
to be embraced therein.
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